text: Nanofluidic diodes are utilized for rectification of ionic transport. A diode in electronic circuits limits the flow of electric current to one direction. A nanofluidic diode has the same function to restrict the ionic flow in one direction. A nanofluidic diode is a channel with its radius dimension of several nanometers. The inner surface of the channel is coated with surface charges. Current rectification can occur when the surface charges at the wall are of the same sign. It is also observed that, when a half of the channel is coated with opposite sign or electrically neutral, the rectification will be enhanced.
  When the wall of the channel is coated with positive charges, the negative charged ions in the electrolyte will be attracted and accumulated within the channel. In this case, the flow of positive charges passing through the channel is not favorable, resulting in a decrease in ionic current. Therefore, the ionic current becomes asymmetric if the biasing voltage is reversed.